This invention relates to an elastic fluid axial flow turbine or compressor and, more particularly, to a lashing structure used with such a turbine or compressor.
An elastic fluid axial flow turbine or compressor comprises a rotor having a peripheral groove and a blade structure comprising an annular row of blades having root portions disposed in the grooves. A variety of techniques for minimizing vibratory stresses in the blade structure have been developed. Groups of blades have commonly been tied together to reduce vibratory stresses. In this technique, at least three blades are secured to each other by means such as a shroud, lashing wires, or both. Preferably the blades are connected together in long arc groups of more than twelve blades per group as described in my prior U.S. Pat. Nos. 4,386,887 and 3,588,278.
It is desirable that the adjacent end blades of the groups be flexibly connected to each other to suppress axio-torsional modes of vibration, as well as improved moisture impingement erosion resistance. A flexible connector used in a lashing wire structure can be a sleeve as shown in FIG. 10 of aforementioned U.S. Pat. No. 4,386,887. To keep the sleeves in the gaps, and to prevent the lashing tie wires from drifting out of position, the sleeves can be welded or brazed to the wires.
However, this technique is not useful where the blades are coated. Turbine blades subjected to cycling between wet and dry are extremely subject to corrosion. To prevent corrosion, the blades can be electroplated, for example, with a nickel-cadmium coating. However, such coatings are adversely affected by the heat required to braze sleeves in place. For example, cadmium when heated above 600.degree. F. can release a toxic vapor. Further a brazed joint on a coated surface has uncertain strength, and thus can fail. Improper brazing also can adversely affect the properties of the coating base metal.
In view of these problems associated with brazing sleeves in places, and the advantages obtained by using sleeves for flexibly connecting lashing wires together, there is a need for a technique to hold such sleeves in position without adversely affecting adjacent coated parts.